Just because it's your opinion doesn't mean you're the only one having it or that you're not right.
So ladies and gentlemen what exactly is a service charge for? If the manager is lying, that's terrible customer service. If he's telling the truth, then why not name it a linen tax.
The problem is that if you ask 10 Jamaicans what a service charge is for they'll give you 10 different answers.
The big deal is that you're letting them walk all over you, the big deal is that you'll never return to that establishment, which means they failed at making you a repeat customer.
The big deal is that countries like Japan have incredible customer service experiences and prohibit Gratuity/service charges!
The big deal is that bad restaurants love people like you that will pay, tip, and leave; and they bank on millions more people like you coming along to keep justifying their prices, their lack of service, and to keep them afloat.